2. CONTENTS
• The structure and function of
nucleus.
• Chromatin structure.
• Structure of nucleus and
nucleolus.
• Structural organization ,levels
of chromatin.
3. INTRODUCTION
• Nucleus is also referred
to as KARYON
• Present in eukaryotic
cells
• Position of the nucleus
is variable and it is
characteristic of the cell.
•
4. MORPHOLOGY
• NUMBER:
• 1. Mononucleate cells- have single nucleus
• 2. Binucleate cells- have two nuclei
• 3. Polynucleate cells- many nuclei
• SHAPE: spheroid, ellipsoid, discoidal
• SIZE: vary from 3 μm to 25 μm in diameter, depends on the
volume of the cell, amount of DNA & proteins and metabolic
phase of the cell.
5. NUCLEUS
• 1. It is membrane-limited
compartment that contains the
genome (genetic information)
in eukaryotic cells.
• 2. COMPONENTS
• A. Chromatin-nuclear material
• B. Nucleolus-DNA, RNA,
proteins
• C. Nuclear envelope- 2
membranes
• Nucleoplasm
6. Nuclear
alterations
• 1. Karyolysis
• the disappearance of nuclei due to complete
dissolution of DNA by increased activity of
DNAase,
• 2. Pyknosis
• condensation of chromatin leading to
shrinkage of the nuclei (they appears as
dense basophilic masses), and
• 3. Karyorrhexis
• fragmentations of nuclei (these changes
usually are proceeded by pyknosis).
7.
8. Nuclear
components
• 1. CHROMATIN
• Complex of DNA & proteins
• Responsible for the characteristic
basophilia of the nucleus.
• Further folding of
chromatin produces structures
called CHROMOSOMES
• Chromatin proteins- Histones,
non histones.
9. TYPES OF
CHROMATIN
2 types
HETEROCHROMATIN- densely staining
material, highly condensed chromatin
EUCHROMATIN- lightly staining
Heterochromatin is disposed in 3 locations:
1. Marginal chromatin-found at the periphery of the
nu- cleus
2. Karyosomes- are discrete bodies of chromatin
irregular in size and shape that are found throughout
the nucleus.
3. Nucleolar associated chromatin- is chromatin found
in association with the nucleolus.
10. Types of
genomic material
in
heterochromatin
1. Constitutive heterochromatin
Similar in all cell types
Contain repetitive, gene poor DNA
sequences- centromere, telomere
2. Facultative heterochromatin
Occurs in Bar body
11. Packaging of
chromatin into
chromosomal
structure
• 1. Nucleosomes
• First level of chromatin folding.
• Formed by coiling of DNA molecules around a core
protein
• Shortens the DNA molecule by approx 7 fold.
• 2. Chromatin fibril
• It is the next step, long strand of nuleosomes is coiled to
form chromatin fibril
• 3. Chromatin fibrils are organized into loop domains
• 4. Heterochromatin- chromatin fibers are tightly packed
• 5. Euchromatin- chromatin fibrils are loosely arranged
• 6. Chromatin is condensed and organized into
chromosomes, in dividing cells.
12.
13. CHROMOSOMES
• 1. CENTROMERE
• Constricted region which connects the 2 arms of
the chromosomes
• 2. Telomere
• Tips of chromosome arms
• 3. TYPES( Based on position of centromere)
• a. Metacentric- centrally placed centromere
• b. Submetacentric- centromere lies between the
centre and end of chromosome
• c. Acrocentric- centromere is located very close
to one end so that the p arm is very small.
• d. Telocentric-Centromere is located at the end.
14. • CHROMOSOMES
• Consist of 2 chromatids joined together by
CENTROMERE
• Human cells have 46 chromosomes organized as 23
homologous pairs(diploid number)
• 22 pairs have identical chromosome- AUTOSOMES
• 23rd pair of chromosome- SEX CHROMOSOME (X and
Y)
• Females -have two X chromosomes
• Males- one X and one Y chromosome
• Diploid number(2n)- somatic cells ( 46 chromosomes)
• Haploid number(n)- ova and sperm (23 chromosomes)
16. NUCLEOLUS
• site of ribosomal RNA (rRNA) synthesis and
initial ribosomal assembly.
• Non-membranous region of the nucleus that
surrounds transcriptionally active rRNA genes.
• It is the primary site of ribosomal production
• three morphologically distinct regions:
• a. Fibrillar centers
• b. Fibrillar material (pars fibrosa)
• c. Granular material (pars granulosa)
17. NUCLEAR ENVELOPE
• 2 MEMBRANES
• INNER- nuclear lamina , chromatin, and ribonucleo- proteins
• OUTER- continuous with the membranes of the endoplasmic reticulum and
can be associated with ribosomes.
• Mutations of lamins-
• Hutchinson-Gilford progeria
• syndrome
•
21. NUCLEAR ENVELOPE
• formed by two membranes with a perinuclear cisternal
space between them.
• separates the nucleoplasm from the cytoplasm.
• provides a selectively permeable membranous barrier between
the nuclear compartment and the cytoplasm,
• 2 membranes- outer and inner with a perinuclear cisternal
space between them.
22. MEMBRANES OF
NUCLEAR ENVELOPE
• 1. The outer nuclear
membrane
• resembles the membrane of the
endoplasmic reticulum
• 2. Inner nuclear membrane
• supported by a rigid net- work
of intermediate protein filaments
attached to its inner surface
called the nuclear (fibrous)
lamina.
23. NUCLEAR LAMINA
• formed by intermediate filaments and lies adjacent to the
inner nuclear membrane.
• Present underneath the nuclear membrane
• FUNCTION
• Support
• Essential in many nuclear activities such as DNA replication,
transcription, and gene regulation.
• COMPONENTS
• nuclear lamins
• lamin- associated proteins.
24. NUCLEOPLASM
• 1. viscous fluid inside the nucleus nuclear envelope
exclusive of the chromatin and the nucleolus.
• 2. Amorphous
• 3. Contents:
• 1. Nucleic acids
• 2. Proteins
• 3. Enzymes, minerals
25. NUCLEOPLASM
1. NUCLEIC ACID
2. PROTEINS
-basic proteins- nucleoprotamines and the nucleohistones.
-Non-histone or Acidic proteins- phosphoprotein
3. ENZYMES- DNA polymerase, RNA polymerase, NAD synthetase, nucleoside triphosphatase,
adenosine diaminase, nucleoside phosphorylase, guanase, aldolase, enolase, 3-phosphoglyceraldehyde
dehydrogenase and pyruvate kinase.
4. LIPIDS
5. MINERALS- phosphorus, potassium, sodium, calcium and magnesium.
26. CHROMATIN FIBERS
• Thread like structures which take up
basic stains
• Observed only in interphase nucleus
• During cell division, they become thick
ribbon like structures called
CHROMOSOMES
• Consists of DNA & proteins like histones.
• It is of two types:
• a. Heterochromatin- darkly stained,
condensed region
• b. Euchromatin- Light stained , diffused
region of the chromatin
27. NUCLEOULUS
• Nuclei has a spherical colloidal acidophilic
body called nucleolus.
• Size depends on synthetic activity of the
cell.
• Position in the nucleus is eccentric
• Chemical composition:
• DNA of nucleolar organizer, four types of rRNAs, 70 types of ribosomal
proteins, RNA binding proteins and RNA splicing nucleoproteins
• phospholipids, orthophosphates and Ca2+ ions.
• enzymes such as acid phosphatase, nucleoside phosphorylase and
NAD+synthesizing enzymes for the synthesis of some co-enzymes,
nucleotides and ribosomal RNA.
